1. Technical Field
The present disclosure relates to telephone communication, and particularly, to a cable modem capable of self-determining to be qualified or unqualified.
2. Description of Related Art
Generally, telephones are connected to a communications network through a cable modem. The cable modem converts network digital signals from the communications network into radio frequency analog signals usable by the telephone and converts radio frequency analog signals from the telephone into network digital signals usable by the communications network. The cable modem includes a subscriber line interface circuit (SLIC) coupled to the telephone. To improve communication quality, an impedance of the SLIC is set substantially equal to (i.e., match) a fixed impedance of the telephone to minimize signal reflection (i.e., noise). However, the impedance of the SLIC may not match that of the telephone. Therefore, it is necessary to detect the presence of noise from a cable modem before practical usage thereof. Such detection is typically carried out by an external detection device, increasing cost and complexity.
Therefore, it is desirable to provide a cable modem which can overcome the limitations described.